In telecommunications systems, it is often desired that a received audio signal be squelched, i.e. suppressed, in the absence of a sufficiently strong desired signal. As an example, in a cordless telephone system, a user of a cordless phone may be a long distance away from the phone's base station when placing a call. A long distance between phone and base station may degrade the wireless signals that are transferred between the phone and base station. In such circumstances, a cordless phone lacking a squelch system would likely output only static or other displeasing noise to the user. In order to enhance the user's experience, a system which squelches the received audio in the absence of a sufficient signal may be employed in the user's cordless phone.
Existing squelch systems may operate by receiving an audio signal, determining the power of out-of-band noise, and utilizing a comparator to determine whether the noise is beyond a certain threshold. If the noise power is beyond the threshold, the system would squelch the audio signal. Similarly, other existing systems may detect the power of out-of-band noise and the power of the audio band signal, and again utilize a comparator to determine whether to squelch the signal. Problems exist with such systems. For example, the former system does not provide the needed control resolution for a high quality audio system and the latter system discriminates unfairly against a received signal with a low audio level but a sufficient carrier-to-noise ratio. Furthermore, these existing systems require power detectors that are not suitable for on-chip integration, and are therefore costly and require a relatively large amount of power to operate. Therefore, it would be useful to have a squelch system that provides finer resolution in the selection of a squelch engagement threshold. It would also be useful to have a squelch system that does not discriminate against a user with a quiet voice. Additionally, it would also be useful to have a squelch system that can be implemented in a mixed-signal DSP environment, which could easily be integrated into a CMOS process.